In general, duct work is commonly used in forced air heating and air-conditioning systems for buildings and the like, with the duct work providing a distribution system to various areas of the building from a furnace and/or air-conditioning system. Coupling a round duct to the furnace or main trunk line is commonly provided via a top take off duct member which is positioned in association with the air handling equipment. The top take off provides the outlet for forced air to exit the trunk line or extended plenum for distribution to the registers. Typically, such a top take off comprises a cylindrical fitting associated with a length of cylindrical tubing which is coupled to an outlet opening in a high pressure plenum of the air handling system. The fitting is installed into and fixed in position with respect to the outlet opening in the wall of a trunk line or plenum. This take off duct can then be coupled into cylindrical duct work which extends to various portions of the building or the like. Depending on the particulars of an installation of an air handling system, it is many times problematic to efficiently couple into the top take off, as the position of the duct work may not correspond to the location of the top take off. Various fittings and interconnections are then necessary to couple the duct work to the air handling system, being a labor intensive and time-consuming process. Attempts to simplify connection of round duct work to a trunk line or plenum have included forming the top take off as an adjustable elbow which allows the orientation and position of the take off to be readily adjusted to simplify positioning and interconnection to the duct system. Such adjustable elbows typically will include three sections, each section being rotatable relative to the others. Each section in the take off is formed so as to be connected at an angular orientation relative to an adjacent section, whereupon relative rotation will vary the orientation of the outlet portion of the take off to simplify coupling into further duct work. Known adjustable take offs may be produced in different ways, but typically utilize a machine which a skilled operator uses for cutting and forming of each of the sections in the take off. Each of the sections may be adjustably coupled to an adjacent section by means of a bead coupling wherein a portion of each section is flared outwardly to engage a similar bead in an adjacent section, thereby locking the pieces together but allowing relative rotation therebetween. Known machines for producing and locking these sections together to form an adjustable take off are problematic, in that many of the stages of production of the sections in the take off are performed manually with a machine for cutting and beading of the take off sections. A skilled operator is therefore necessary to properly form each section and couple the sections together in a manner that they can be adjusted to one another. The difficulty of properly forming each section and connecting the sections together result in a high percentage of scrap as well as take offs which do not function well. More recently, automated take off machines have been produced which are designed to form straight take offs, wherein a cylindrical tube is cut into multiple pieces with the pieces being reassembled and locked together in an adjustable coupling. Although such apparatus is capable of forming a more uniform adjustable coupling between sections of the take off in a repeatable fashion, only straight take offs are able to be manufactured, with each section of the take off having a common diameter.
Other problems associated with these machines include the loss of air through the beads between the gores of the duct system. As air circulates through the duct system, air dissipates through the beads or seams that are between the gores, which in turn, causes a loss of energy and thus creates a less efficient system. Presently, no apparatus or methods exist for automated manufacture of adjustable ducts that are highly efficient with respect to the leakage that occurs at the beads or seams of the duct system.